Problem: Let N be a positive odd number.

There are N coins, numbered 1, 2, \ldots, N. For each i (1 \leq i \leq N), when Coin i is tossed, it comes up heads with probability p_i and tails with probability 1 - p_i.

Taro has tossed all the N coins. Find the probability of having more heads than tails.

Constraints

* N is an odd number.
* 1 \leq N \leq 2999
* p_i is a real number and has two decimal places.
* 0 < p_i < 1

Input

Input is given from Standard Input in the following format:


N
p_1 p_2 \ldots p_N


Output

Print the probability of having more heads than tails. The output is considered correct when the absolute error is not greater than 10^{-9}.

Examples

Input

3
0.30 0.60 0.80


Output

0.612


Input

1
0.50


Output

0.5


Input

5
0.42 0.01 0.42 0.99 0.42


Output

0.3821815872

Solution (in CPP):

Solution:
#include <bits/stdc++.h>
using namespace std;
double a[3000],f[3000][3000];
int main()
{
	int i,j,n;
	double ans=0.0;
	scanf("%d",&n);
	f[0][0]=1;
	f[0][1]=0;
	for(i=1;i<=n;i++)
	{
		scanf("%lf",&a[i]);
		f[i][0]=f[i-1][0]*(1-a[i]);
	}
	for(i=1;i<=n;i++)
		for(j=1;j<=i;j++)
			f[i][j]=f[i-1][j]*(1-a[i])+f[i-1][j-1]*a[i];
	for(i=(n+1)/2;i<=n;i++)
		ans+=f[n][i];
	printf("%.10lf",ans);
	return 0;
}